function downloadFile(blob,fileName) {
    if (blob!=null){
        if ('download' in document.createElement('a')) { // 不是IE浏览器
            let url = window.URL.createObjectURL(blob);
            let link = document.createElement('a');
            link.style.display = 'none';
            link.href = url;
            link.setAttribute('download', fileName);
            document.body.appendChild(link);
            link.click();
            document.body.removeChild(link); // 下载完成移除元素
            window.URL.revokeObjectURL(url) // 释放掉blob对象
        } else { // IE 10+
            window.navigator.msSaveBlob(blob, fileName);
        }
    }

}

